A technology with the potential to create efficient and compact refrigeration devices is an active magnetic regenerative refrigerator (AMRR). AMRRs exploit the magnetocaloric effect displayed by magnetic materials whereby a reversible temperature change is induced when the material is exposed to a change in applied magnetic field. By using the magnetic materials in a regenerator as the heat storage medium and as the means of work input, one creates an active magnetic regenerator (AMR). Although several laboratory devices have been developed, no design has yet demonstrated the performance, reliability, and cost needed to compete with traditional vapor compression refrigerators. There are many reasons for this and questions remain as to the actual potential of the technology. The objective of the work described in this thesis is to quantify the actual and potential performance of a permanent magnet AMR system. A specific device configuration known as a dual-nested-Halbach system is studied in detail. A laboratory scale device is created and characterized over a wide range of operating parameters. A numerical model of the device is created and validated against experimental data. The resulting model is used to create a cost-minimization tool to analyze the conditions needed to achieve specified cost and efficiency targets. Experimental results include cooling power, temperature span, pumping power and work input. Although the magnetocaloric effect of gadolinium is small, temperature spans up to 30 K are obtained. Analysis of power input shows that the inherent magnetic work is a small fraction of the total work input confirming the assumption that potential cycle efficiencies can be large. Optimization of the device generates a number of areas for improvement and specific results depend upon targeted temperature spans and cooling powers. A competitive cost of cooling from a dual-nested-Halbach configuration is challenging and will depend on the ability to create regenerator matrices with near-ideal adiabatic temperature change scaling as a function of temperature. / Graduate / 0548 / 0791 / 0607 / atura@uvic.ca

Magnetocaloric materials with first-order magnetic (FOM) phase transitions are of interest as low-cost working materials in magnetic cycles. Hysteresis is a property associated with first order transitions, and is undesirable as it can reduce performance. Devices using FOMs in active magnetic refrigeration have shown performance comparable to more expensive second-order materials, so some degree of hysteresis appears to be acceptable; however, the amount of hysteresis that may be tolerated is still an unanswered question. Among the FOM, the family of MnP-based is one of the promising materials for magnetic heat pump applications near room temperature. The present study describes the experimental investigation of a single-layer MnFeP1-xSix active magnetic regenerator (AMR), under different test conditions and following a protocol of heating and cooling processes. The results for the FOM are compared with a Gd AMR that is experimentally tested following the same protocol, with the objective to study the irreversibilities associated with FOM. The experimental tests are performed in a PM I test apparatus at a fixed displaced volume of 5.09 cm3 and a fixed operating frequency of 1 Hz. The results indicated a significant impact of the hysteresis on the heating and cooling temperature span for FOM regenerator. For certain operating conditions, multiple points of equilibrium (MPE) exist for a fixed hot rejection temperature. It is shown that the existence of MPEs can affect the performance of an AMR significantly for certain operating conditions. The present work advances our understanding since the combined hysteresis and MPE are two significant features which can impact layered AMR performance using MnFeP1-xAsx FOM by systematic experimental testing. With this objective, three multilayer MnFeP1-xAsx FOM regenerator beds are experimentally characterized under a range of applied loads and rejection temperatures. Thermal performance and the impacts of MPE are evaluated via heating and cooling experiments where the rejection (hot side) temperature is varied in a range from 283 K to 300 K. With fixed operating conditions, we find multiple points of equilibrium for steady-state spans as a function of warm rejection temperature. The results indicate a significant impact of MPE on the heating and cooling temperature span for multilayer MnFeP1-xAsx FOM regenerator. Unlike single material FOM tests where MPEs tend to disappear as load is increased (or span reduced), with the layered AMRs, MPEs can be significantly even with small temperature span conditions. A third experimental study examines the performance of MnFeP1-xAsx multilayer active magnetic regenerators. Five different matrices are tested: (i) one with three layers; (ii) one with six layers; and (iii) three, eight layer regenerators where the layer thickness is varied. The tests are performed using a dual regenerator bespoke test apparatus based on nested Halbach permanent magnets (PM II test apparatus). Operating variables include displaced volume (3.8 - 12.65 cm3), operating frequency (0.5 - 0.8 Hz) and hot-side rejection temperature (293-313 K).The results are mainly reported in terms of zero net load temperature span as a function of rejection temperature; a few tests with non-zero applied load are also presented. A maximum temperature span of 32 K is found for an 8-layer regenerator, which is similar to a previous work performed with gadolinium in the same experimental apparatus. A 1D active magnetic regenerator model accounting for thermal and magnetic hysteresis is developed and compared to experimental data for both a Gd-based and MnFeP1-xSix based AMR. Magnetic and thermal hysteresis are quantified using measured data for magnetization and specific heat under isothermal and isofield warming and cooling processes. Hysteresis effects are then incorporated in the model as irreversible work and reduced adiabatic temperature change. Model results are compared to measured temperature spans for regenerators operating with different thermal loads. Simulated results for temperature span as a function of cooling power and rejection temperature show good agreement with experimental data. The irreversible work due to hysteresis is found to have a small impact on predicted spans, indicating that useful cooling power is well predicted using cyclic measurements of adiabatic temperature change. / Graduate

L’objectif de ce travail est de développer un modèle multi-physique et multi-échelle de Régénérateur Magnétique Actif en vue d’optimiser le fonctionnement d’un système de réfrigération magnétique. Le modèle numérique développé lors de cette thèse est un modèle multi-physique et multi-échelle qui prend en compte trois phénomènes distincts (le magnétisme, la fluidique et le transfert de chaleur), chacun à une échelle différente (micro-échelle, mini-échelle et macro-échelle). Une étude expérimentale a été menée afin de déterminer les propriétés thermophysiques des matériaux magnétocaloriques et d’intégrer les résultats de ces mesures dans le modèle numérique. Le modèle a été validé par une comparaison avec des données expérimentales et les résultats obtenus ont montré une bonne corrélation entre les résultats du modèle et les mesures. Enfin, le modèle a été exploité par une analyse de sensibilité des paramètres en vue d’étudier le fonctionnement ainsi que les performances du système. Ce modèle permettra d’identifier une stratégie de conception optimale d’un Régénérateur Magnétique Actif afin de concevoir des systèmes de réfrigération magnétique performants. / The objective of this work is the developing of a multi-physics and multi-scale numerical model of an Active Magnetic Regenerator in order to optimize the operation of a magnetic refrigeration system. The numerical model developed in this thesis is a multi-physics and multi-scale model that takes into account simultaneously three distinct phenomena (magnetism, fluid flow and heat transfer), each on a different scale (micro-scale, mini-scale scale and macro-scale). An experimental study was conducted to determine the thermophysical properties of magnetocaloric materials and integrate the results of these measurements in the numerical model. The model has been validated by comparison with experimental data and the results showed a good correlation between the model results and measurements. Finally, the model was exploited by an analysis of parameter sensitivity allowing studying the operation and performance of the system. This model will identify an optimal design strategy of an Active Magnetic Regenerator in order to design high-performance magnetic refrigeration systems.

La réfrigération magnétique est une alternative pertinente dans un contexte où les gaz réfrigérants sont soumis à des restrictions environnementales. Ces restrictions nécessitent l'évolution de la technologie actuelle ou bien l'émergence d'une nouvelle, d'où l'opportunité pour la réfrigération magnétique de prouver son potentiel. En effet, elle pourrait s'avérer énergiquement plus efficace et avec des densités de puissance supérieure. Ces travaux de thèse apportent des réponses sur le potentiel de la réfrigération magnétique. Dans cette logique, la thermodynamique et le magnétisme, outils indispensables à notre étude, sont développés dans le cas des matériaux à effet magnétocalorique. Puis, nous verrons que les caractérisations de ces derniers sont en mesure de fournir des modèles matériaux cohérents et réalistes, si des précautions sont prises. L'effet magnétocalorique étant limité en termes de variation de température, nous allons étudier différentes structures de réfrigération. Enfin, des modèles numériques sont développés pour permettre d'optimiser les structures à régénérations actives, qui sont les plus utilisées. Ces modèles doivent permettre de dimensionner des systèmes proches de leurs optimums. / Magnetic refrigeration is a relevant alternative in consideration of environmental restrictions of refrigerants gases. These restrictions require to improve the current technology or to pave the way for a new one, hence the opportunity for magnetic refrigeration to demonstrate its potential. Indeed, it could be energetically efficient and with higher power densities. This work aims to estimate the potential of magnetic refrigeration. Magnetism and thermodynamic, essential tools for our study, are developed in a case of magnetocaloric effect. With some care, we show that material characterizations are able to give consistence and relevant model. Magnetocaloric effect suffers of small temperature variations; therefore structures that increase the temperature span and give competitive system are studied. Finally numerical models are developed to optimize active magnetic regenerators, which are currently the most used. These models are used to calculate and design systems close to their optimum.

No description available.

La réfrigération magnétique est une technologie émergente grâce à des avantages considérables par rapport aux technologies de réfrigération classiques. Cette technologie basée sur l’effet magnétocalorique offre d’importants avantages environnementaux car d’une part l’efficacité théorique des cycles utilisés est supérieure à celle des technologies classiques et d’autre part son fonctionnement ne nécessite pas une utilisation de gaz/vapeur `a fort effet de serre. En revanche des verrous scientifiques restent à lever, Le modèle multi-physique proposé dans cette thèse à pour but d’améliorer la précision de calcul. Il consiste à coupler un modèle 3D magnétostatique résolu par la méthode des éléments finis, un modèle magnétocalorique analytique et un modèle thermo-fluidique résolu par méthode des différences finies. Parallèlement, un banc d’essais a été conçu, optimisé et réalisé, ce banc permettra de faire des mesures fines des différents phénomènes qui interagissent dans la réfrigération magnétique. / The magnetic refrigeration technology is a promising alternative technology to the production of cold. The work of this thesis deals with studying and designing a magnetic refrigeration prototype. A multiphysic model is developed, this model taking into account several magnetic and magnetocaloric aspect that never dealt in the literature. It is used to investigate the influence of a range of parameters on the performance of the AMR. A new test bench of magnetic refrigeration is also designed, it is based on a particular electromagnet that was optimally realized. The magnetic performances are showed and concord with design prevision. Finally, suggestions for future works are provided based on the knowledge presented here.

Energy conversion devices using solid-state magnetocaloric materials have the potential to reduce energy consumption and mitigate environmental pollutants. To overcome the limited magnetic entropy change of magnetocaloric materials, magnetic refrigeration devices typically use the active magnetic regenerator (AMR) cycle. AMR devices have demonstrated promising performance, however costs must be reduced for broad market penetration. Although the magnet cost is of greatest importance for commercialization, literature has decoupled magnet design from AMR optimization. And while multilayered regenerators can improve performance without increasing cost, a number of questions remain unanswered as a result of the prohibitive parameter space. This dissertation explores methods of improving AMR performance and decreasing cost both at the subsystem level, namely the magnetocaloric regenerator, fluid flow system and magnetic field source, and the device level by coupling the regenerator and magnet design problems in a cost optimization framework. To improve AMR performance, multilayered regenerators with second-order magnetocaloric materials are experimentally and numerically investigated, yielding insight on how individual layers behave and interact over a wide range of regenerator compositions and operating parameters. An efficient AMR modeling approach is presented where individual layers are treated as cascaded AMR elements, and simulations are in excellent agreement with experiments. Insights from the computationally efficient model are used to inform device modifications, and a no-load temperature span of 40 K is measured in close proximity to the simulated optimum; one of the highest in literature. To simultaneously decrease AMR costs, a permanent magnet optimization framework is explored that is conducive to nonlinear objectives and constraints. This is used to investigate the optimal design of permanent magnet structures with reduced rare-earth permanent magnet materials. The regenerator and magnet design problems are then coupled in a permanent magnet topology optimization to minimize the combined capital and operating costs of an AMR. The optimal magnetic field waveform and the optimal means of producing this waveform are simultaneously obtained. The lifetime ownership costs of the optimized AMR device are shown to be in the realm of existing entry-level cooling devices. The presented cost optimization framework is of interest to both scientists and engineers, and demonstrates the importance of fast AMR models in identifying system designs, regenerator compositions and operating regimes that increase AMR performance and decrease cost. / Graduate

[EN] This PhD thesis studies the application of the magnetic refrigeration technology in the air-conditioning system of automobiles. Thermal models of each of the components of such a system have been developed with the purpose of determining accurately its global performance. A dynamic one-dimensional model of a parallel-plate active magnetic regenerator (AMR) has been developed. The model is based in a new numerical scheme that reduces the computation time by 88% compared to the most commonly employed method. The model reproduces very accurately the passive regenerator cases with analytic solution and has been thoroughly validated against experimental results of both passive regenerator and AMR tests. The inclusion in the model of the magnetocaloric properties experimentally measured with a sample of the employed material, the demagnetizing effect, the fluid flow maldistribution and the losses to the ambient in the experimental setup have all been keys to obtain a good agreement with the experiments. The influence of the uncertainties and simplifications assumed when modelling these physical phenomena has been analyzed in detail, which has allowed the validation of different approaches. Besides, a dynamic model of the air-conditioning (AC) system of an electric vehicle has been developed. Thermal models of each of the system components have been included, namely the cabin, the hydraulic loops with the air-to-coolant heat exchangers and the electric auxiliaries. The modelling methodology employed is based on the combination of the conservation equations with the semi-empirical fitting of the global heat transfer coefficient. Excellent validation results have been obtained with experimental results in a wide range of operating conditions. The vehicle model has been employed to obtain the cooling and heating demand of a commercial full electric minibus, as well as the working temperatures. A broad optimization study has been carried out with the AMR model with the purpose of determining the design and working parameters of such a refrigerator that fulfil the cooling requirements of the vehicle with a minimum combined total system mass (affecting the weight of the vehicle and the economic cost) and electric consumption. The electric demand of the electrical AC auxiliaries has also been considered. Additionally, the heating performance of the optimal designs has been calculated. The application of AMR refrigerators in mobile air-conditioning systems is analyzed in comparison to the features of current vapor-compression systems. / [ES] En la presente tesis doctoral se ha estudiado la aplicación de un refrigerador magnético en un sistema de aire acondicionado para automóviles. Con el fin de determinar las prestaciones de dicho sistema de manera global y precisa, se ha desarrollado un modelo térmico de cada uno de sus componentes. Por un lado, se ha desarrollado un modelo dinámico unidimensional de regenerador magnético activo (AMR) de placas planas paralelas, basado en un nuevo esquema numérico que reduce el tiempo de cálculo hasta en un 88% respecto al esquema más empleado. El modelo reproduce con gran exactitud los casos de regenerador con solución analítica y ha sido validado exhaustivamente con resultados experimentales funcionando como regenerador pasivo y como AMR. Para obtener buenos ajustes ha sido clave la inclusión en el modelo de las propiedades magnetocalóricas medidas experimentalmente con una muestra del material empleado, el efecto desmagnetizante, la mala distribución del fluido y las pérdidas hacia el ambiente del montaje experimental. La influencia de las incertidumbres y las simplificaciones en el modelado de estos fenómenos se ha analizado detalladamente, lo cual ha permitido validar diferentes aproximaciones. Por otro lado, se ha desarrollado un modelo dinámico del sistema de aire acondicionado de un vehículo eléctrico. Se incluye el modelo térmico de la cabina, los bucles hidráulicos para la distribución de la potencia térmica con los intercambiadores de calor agua-aire y los auxiliares eléctricos. La metodología empleada para el desarrollo de estos modelos, basada en la combinación de ecuaciones de conservación con el ajuste semi-empírico de los coeficientes globales de transmisión de calor, ha producido excelentes resultados de validación con resultados experimentales en un amplio rango de condiciones de funcionamiento. El modelo del vehículo se ha empleado para obtener la demanda de refrigeración y calefacción de un minibús eléctrico comercial, así como las temperaturas de funcionamiento del sistema. Con el modelo de AMR se ha llevado a cabo un amplio estudio de optimización para determinar los parámetros de diseño y de funcionamiento de dicho refrigerador que cubren las necesidades de refrigeración del vehículo una masa del conjunto del sistema y un consumo eléctrico mínimos, incluyendo el consumo de los auxiliares. Adicionalmente se han calculado las prestaciones de calefacción de las combinaciones óptimas. La aplicabilidad de este sistema en automóviles se analiza en comparación con un sistema equivalente de compresión de vapor. / [CA] En aquesta tesi doctoral s'ha estudiat l'aplicació d'un refrigerador magnètic en un sistema d'aire condicionat per a automòbils. A fi de determinar les prestacions d'aquest sistema de manera global i precisa, s'ha desenvolupat un model tèrmic de cadascun dels components. D'una banda, s'ha desenvolupat un model dinàmic unidimensional de regenerador magnètic actiu (AMR) de plaques planes paral·leles, basat en un nou esquema numèric que redueix el temps de càlcul fins d'un 88% respecte a l'esquema més emprat. El model reprodueix amb gran exactitud els casos de regenerador amb solució analítica, i ha sigut validat exhaustivament amb resultats experimentals funcionant com a regenerador passiu i com a AMR. Per a obtenir bons ajustos ha sigut clau la inclusió en el model de les propietats magnetocalòriques mesurades experimentalment amb una mostra del material emprat, l'efecte desmagnetitzador, la mala distribució del fluid i les pèrdues cap a l'ambient del muntatge experimental. La influència de les incerteses i les simplificacions en la modelització d'aquests fenòmens s'ha analitzat detalladament, la qual cosa ha permès validar diferents aproximacions. D'altra banda, s'ha desenvolupat un model dinàmic del sistema d'aire condicionat d'un vehicle elèctric. S'hi inclouen el model tèrmic de la cabina, els bucles hidràulics per a la distribució de la potència tèrmica amb els bescanviadors de calor aigua-aire i els auxiliars elèctrics. La metodologia emprada per al desenvolupament d'aquests models, basada en la combinació d'equacions de conservació amb l'ajust semiempíric dels coeficients globals de transmissió de calor, ha produït excel·lents resultats de validació amb resultats experimentals en un ampli rang de condicions de funcionament. El model del vehicle s'ha emprat per a obtenir la demanda de refrigeració i calefacció d'un minibús elèctric comercial, així com les temperatures de funcionament del sistema. Amb el model d'AMR s'ha dut a terme un ampli estudi d'optimització per determinar els paràmetres de disseny i de funcionament de la refrigeradora esmentada que cobreixen les necessitats de refrigeració del vehicle, una massa del conjunt del sistema i un consum elèctric mínims, incloent el consum dels auxiliars. Addicionalment s'han calculat les prestacions de calefacció de les combinacions òptimes. L'aplicabilitat d'aquest sistema en automòbils s'analitza comparant-la amb la d'un sistema equivalent de compressió de vapor. / Torregrosa Jaime, B. (2016). Modelling and analysis of an air-conditioning system for vehicles based on magnetocaloric refrigeration [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68503 / Premios Extraordinarios de tesis doctorales